| MGS Global Consulting Ltd | Information & communication | 2025 |
| MGS Heating Ltd | Construction | 2021 |
| MGW Support LLP | | 2022 |
| MH Locum Services Ltd | Health & social care | 2021 |
| MH Photography Limited | Professional & scientific | 2019 |
| MH Recovery Limited | Professional & scientific | 2017 |
| MH Surgimed Ltd | Health & social care | 2016 |
| MHK Highways Limited | Construction | 2022 |
| MHP Construction Limited | Construction | 2006 |
| MHP Property Management Limited | Hospitality | 2016 |
| MI Amor Retreat Ltd | Other services | 2022 |
| MIA Aesthetics Ltd | Other services | 2022 |
| MIA by Design Ltd | Professional & scientific | 2022 |
| MIA Partners Ltd | Administrative & support | 2022 |
| Mia-Zion Ltd | Health & social care | 2016 |
| Mibootcamp Ltd | Arts & recreation | 2025 |
| Mich Linen Ltd | Other services | 2024 |
| Michael Doyle Engineering Ltd | Manufacturing | 2016 |
| Michael J Bailey Limited | Construction | 2012 |
| Michael J. Wilkinson & Co Limited | Professional & scientific | 2000 |
| Michael James Smith Ltd | Arts & recreation | 2017 |
| Michael Linnell and Co. Ltd | Manufacturing | 2000 |
| Michael Neenan Limited | Other services | 2002 |
| Michael Shellim Design Limited | Construction | 2011 |
| Michael Shellim Investments Limited | Real estate | 2011 |
| Michael Stuart & Sons Contractors Limited | | 1989 |
| Michael's Cleaning Services Ltd | Administrative & support | 2026 |
| Michel Herbelin U.K. Limited | Wholesale & retail | 1981 |
| Michelle Mcgagh Limited | Information & communication | 2012 |
| Mick & Bill's Meals on Wheels Ltd | Hospitality | 2026 |
| Mick Everitt Roofing & Welding Services Ltd | Construction | 2009 |
| Micro Lithography Services Limited | Manufacturing | 2009 |
| Microtill Limited | Wholesale & retail | 2007 |
| Mid-Essex Skin Cancer Service Limited | Health & social care | 2020 |
| Middlesex Fencing Ltd | Administrative & support | 2026 |
| Midnight Pizza Ltd | Hospitality | 2025 |
| Midnight River Media Ltd | Information & communication | 2026 |
| Midnight Sun Construction Limited | Construction | 2018 |
| Miella Collection Limited | Wholesale & retail | 2025 |
| Migo Consultancy Limited | Professional & scientific | 2010 |
| Migo Properties Limited | Real estate | 2025 |
| Mihaelaast Limited | Health & social care | 2019 |
| Mikenmo Ltd | Professional & scientific | 2026 |
| Miki Express Ltd | Transport & logistics | 2022 |
| Miko & Moon Fire Protection Ltd | Construction | 2021 |
| Mila Bar & Grill Limited | Hospitality | 2024 |
| Milada Online Trading Limited | Wholesale & retail | 2024 |
| Miladi Ltd | Wholesale & retail | 2026 |
| Milbrooke Motors Limited | Wholesale & retail | 1992 |
| Milbury Meats & Hams Limited | Wholesale & retail | 2000 |
| Milcra Airfield Solutions Limited | Construction | 2015 |
| Milecastle Media Limited | Administrative & support | 2014 |
| Miles Rental Limited | Administrative & support | 2025 |
| Milez Entertainment Ltd | Information & communication | 2025 |
| Milford Capital Limited | Professional & scientific | 2006 |
| Milk Bar Limited | Wholesale & retail | 2002 |
| Milkdale Ltd | Wholesale & retail | 2024 |
| Mill Park Investments Limited | Administrative & support | 2006 |
| Millennium International Forwarding Limited | Transport & logistics | 1998 |
| Miller Environmental Solutions Limited | Professional & scientific | 2018 |
| Miller GEM Consulting Limited | Professional & scientific | 2024 |
| Millertree Ltd | Professional & scientific | 2019 |
| Million Dollar YOU Ltd | Other services | 2017 |
| Millquick Ltd | Real estate | 1998 |
| Millrace Furniture Restoration Co-Operative Ltd | Manufacturing | 1995 |
| Mills Mowing and Maintenance Ltd | Households | 2023 |
| Mills Property Management Services Ltd | Real estate | 2025 |
| Millwell Residents Association Limited | Households | 1992 |
| Milo Estate Management Limited | Real estate | 2022 |
| Mimodo Architects Ltd | Professional & scientific | 2009 |
| Mimosa Beauty Limited | Other services | 2016 |
| Mimosa Studio Ltd | Wholesale & retail | 2021 |
| Minami (Maldon) Ltd | Extraterritorial | 2022 |
| Mind and Body Connections Ltd | Public administration | 2023 |
| Mindal Limited | Information & communication | 2001 |
| Mindscript Limited | Information & communication | 2018 |
| Mindset Mentors Limited | Other services | 2016 |
| Minerva Fund Management Solutions Limited | Financial services | 2019 |
| Mingutz Ltd | Transport & logistics | 2016 |
| Mini Wonders Children's Physiotherapy Ltd | Health & social care | 2020 |
| Minime Mindfulness CIC | Education | 2025 |
| Ministry Protective Ltd | Administrative & support | 2019 |
| Mint Controls Limited | Construction | 2017 |
| Mintos Marketplace Ltd | Financial services | 2015 |
| Miracles Everyday Limited | Education | 2023 |
| Miran Kebab Ltd | Hospitality | 2026 |
| Mirli Books Limited | Information & communication | 2009 |
| Mirror Image Salon Limited | Other services | 2015 |
| Mirta Ltd | Health & social care | 2017 |
| MIS Construction Services Ltd | Manufacturing | 2018 |
| Mischievous Media Ltd | Information & communication | 2001 |
| Miss Geek Limited | Wholesale & retail | 2025 |
| Miss Rachel Holland Ltd | Other services | 2020 |
| Miss UK Nails Ltd | Real estate | 2017 |
| Mission: Forward Ltd | Wholesale & retail | 2025 |
| Mister COD Ltd | Hospitality | 2026 |
| Mister Gees Foundation (Trading) Limited | Wholesale & retail | 2017 |
| Mister PC Limited | Information & communication | 2008 |
| Misue Linen Limited | Other services | 2001 |
| Mitchell Future & Options Advisers Ltd | Financial services | 2014 |